WORLD OF INDUSTRIES 01/2019

Electric drive systems

Electric drive systems for offshore cranes The most common type of drive technology on ships and offshore platforms has been the hydraulic drives. With increase in safety requirements and environmental regulations becoming more stringent, the electric drive technology has become a key area of focus. In co-operation with the German gear manufacturer O&K Antriebstechnik, offshore pedestalmounted lattice boom cranes with innovative electric drive concept were recently commissioned by Palfinger Marine. 01 The four drives of the cable winch within the lattice boom are arranged face to face in the steel lattice boom crane made by Palfinger Marine MOTION AND DRIVES 14 WORLDOFINDUSTRIES 1/2019

The overall mechanical requirements of the project have sparked the ambition of the engineers. For steel lattice boom cranes with a reach of up to 57 m and a safe working load of 60 t, the aim was to develop the most compact electric drives possible for the main winch and boom winch. The steel lattice structure of the crane boom strictly dictated the respective installation spaces, for safety reasons, nothing could protrude beyond the lattice structure. At the same time, the size of the crane also dictated the cable thicknesses and lengths, as well the dimensions of the drum. In conjunction with the necessary torques and motor outputs, it quickly became clear that the performance requirements could not be met within the available space by a simple electrical drive. The constructional task was thus to distribute the power to several motors on the one hand, while transferring the total torque to the winch drum on the other. Tight installation space requires particular layout The calculations within the given framework conditions resulted in the drive of the rope winch that operates the hook being divided into four electric motors of size IEC 280, each with a weight of approximately 1.2 t. The boom winch has two motors of size IEC 315, each with a weight of approximately 1.7 t. This determined the entrance side, but there was still a constructional task left to tackle: The effective layout and connection of the motors to the winch system. It was not only the transmission of drive power that had to be considered but also the size and weight of the motors themselves. The special asynchronous motors, at about 2 m long and with the above stated heavy weight per engine, are not insignificant. When it comes to load distribution of the drive, which occurs via electronic control, then the purely mechanical elements must also be safely arranged in a purely constructional manner. The mechanical solution from O&K Antriebstechnik consists of two components each on both sides of the drum: a motor flange and an angle system flowing into the actual winch system. For the boom winch, the angle gear is designed in such a way that a fail-safe brake is mounted opposite the engine’s power side for emergency situations. This ensures that the crane boom remains in position and cannot sag, even when there is an interruption in power, a significant safety aspect. With a high degree of efficiency, a bevel gear setup transfers the motor input torque to the winch’s planetary gear, which is located in the winch drum. The winch itself can be found at the crane tower and experiences only the rotational movements of the tower. There should be no anomalies when lubricating the angular gear. A control system ensures synchronous operation of the drives on both sides of the winch. The large cable winch drum, which has a width of around 2 m, is mounted near the tower in the boom of the crane. The four drives of the cable winch are also arranged on both sides of the winch drum, with two drives apiece directly facing each other. These motors are also mounted with a motor flange on an angular gear, which transfers the combined power of the two motors, which are joined at right angles, to the planetary gear that is integrated into the winch drum. Of particular importance here is the sophisticated lubrication system of the bevel gear setup, which ensures that the lubricant is supplied to the best possible degree, irrespective of the position of the boom. The four motors, which are also inverter-fed, work in perfect synchronization with each other. Complete electrification offers clear advantages Together with the electric rotary drives, the boom crane is thus completely electrically driven. The control system is at the cutting edge of current technology, operates and reacts quickly and ensures safety up to a significant wave height of up to 6 m, which can only be reached during stormy winds. The electrical drives are also advantageous in terms of flexibility in operation and even enable remote access to the crane, which can be implemented for fault detection and fast support, for example. In addition, standard components are used to a large extent, which enables easy maintenance and fast supply of spare parts. In all, the electric drives provide a higher level of energy efficiency, thus ensuring lower energy consumption and practically eliminating the risk of oil contamination that could occur due to a breakdown or accident involving the hydraulic system. These electric drives have proven themselves completely effective in other industries that operate in harsh environmental conditions. In construction machinery, they can provide service in their role as travel or slewing drives that is just as reliable as it is when they are used in wind turbines around the globe and under extreme weather conditions. Developed in accordance with strict EN13852-1 and Norsok R002 standards, they reliably fulfill all requirements, even in offshore applications. The cranes that are equipped with electric drive technology have less wear-prone components, which therefore means they also have lower maintenance costs. Above all, however, they work much more quietly and produce noticeably less vibration. So there are many reasons for implementing this change. Know-how and experience are fundamental The specially designed drive components were implemented by engineers from German drive technology experts O&K Antriebstechnik. In close co-operation with colleagues from machinery manufacturers, they have developed and designed machine-specific solutions in a surprisingly short period of time. After a thorough range of tests that are tailored towards the requirements of a specific application, the product will go into serial production ensuring reliable supply to customers. Photographs: Palfinger Marine/Bonfiglioli 02 The steel lattice structure of the crane boom strictly dictated the installation space of the winch drives in the crane of Palfinger Marine www.bonfiglioli.com/en WORLDOFINDUSTRIES 1/2019 15